small notepad and pen/pencil for keeping track of life totals, and other notes (e.g. Bomb cards/removal your opponent uses in game 1, or sideboard notes)
I would really recommend a deck box. I like the Ultra-Pro Satin Tower. It should only run you 10$ or so, and has a nice bottom compartment for your dice/counters.
Sleeves. Whatever brand you want. Protect your cards, and makes it easier to shuffle your deck.
Water/Snacks. You will be there for a while, plan accordingly.
And have fun.
For a single deck I tend to like Ultra Pro Satin Towers or Ultimate Guard Xenoskins (there's also a double version and smaller versions).
For something smaller I like Ultimate Guard Boulders which I store in Ultimate Guard Arkhive.
The Professor, on the Youtube Channel Tolarian Community College does pretty good product reviews for tons of deck boxes and sleeves and such.
If you know they're working on a particular Commander deck, I've heard good things about Alter Sleeves.
People generally like Dragon Shield matte sleeves, that you can buy from CardKingdom here and here.
Ultra Pro Satin Tower Deck Box are pretty great, and you can buy them from Amazon. You could also browse Etsy for something made out of wood / more interesting than plastic.
I like to use dice as counters, so you could get some nice dice from Die Hard Dice.
These only go up about 1/2 way on the deck. Might work?
https://www.amazon.com/Ultra-Pro-Black-Satin-Tower/dp/B00FRIE76I
Do you know if the minis would work/fit in this deck box?